DEFINITION
Using a biological agent -- commonly filter feeders (bivalves) such as oysters, bacteria, or plants -- to remove undesirable substances from the water. Biological filters containing multiple species of bacteria have been used in saltwater aquariums. Seeding an estuary or aquaculture pond with oysters to improve the water quality is another approach.

AKA
Oyster filter, bacterial filter, biofiltration, biostrips, biobags

PERFORMANCE CRITERIA
Performance criteria measure the concentration of the undesirable substance in the water after passing through the biological filter in addition to the difference in the concentration of the undesirable substance in the water before and after passing through the biological filter (e.g. removal efficiency).
Typically, biofilters are established to remove sediments, pollutants and/or odors.

Many devices have been developed by the commercial sector to mimic natural processes.
The key is to maximize removal efficiency, while minimizing maintenance (time & filter media) costs.


ILLUSTRATION

Photo of a bay filled with oysters, a filter feeder that can be used as a biological filter. Photo courtesy Sarasota County Government.



CASE STUDIES
links to separate pages documenting specific places or projects where this element is on display

ADDITIONAL RESOURCES
http://www.nytimes.com/2008/02/24/nyregion/24oysters.html

A significant amount of research has looked into the use of oysters as biological filters. Some papers of interest include:

1. Kimberly A. Nelson, Lynn A. Leonard, Martin H. Posey, Troy D. Alphin, Michael A. Mallin, Using transplanted oyster (Crassostrea virginica) beds to improve water quality in small tidal creeks: a pilot study, Journal of Experimental Marine Biology and Ecology, Volume 298, Issue 2, Anthropogenic Influences on the Ecology of Tidal Creeks and Canals, 28 January 2004, Pages 347-368, ISSN 0022-0981, DOI: 10.1016/S0022-0981(03)00367-8. (http://www.sciencedirect.com/science/article/B6T8F-49H1S7R-4/2/9e106f27e300cb591f20f7a999a46d46)
2. Muki Shpigel, Robert A. Blaylock, The Pacific oyster, Crassostrea gigas, as a biological filter for a marine fish aquaculture pond, Aquaculture, Volume 92, 1991, Pages 187-197, ISSN 0044-8486, DOI: 10.1016/0044-8486(91)90020-8. (http://www.sciencedirect.com/science/article/B6T4D-49NPN8M-1MC/2/7bc3ac4925ae4137d56f1e8436e22ae2)
3. Yao-Xing Liu, Tong Ou Yang, Dong-Xing Yuan, Xiao-Yun Wu, Study of municipal wastewater treatment with oyster shell as biological aerated filter medium, Desalination, Volume 254, Issues 1-3, 15 May 2010, Pages 149-153, ISSN 0011-9164, DOI: 10.1016/j.desal.2009.12.003. (http://www.sciencedirect.com/science/article/B6TFX-4Y41MGD-2/2/e04121c149554f5f086e6965ac7c0b64)